Driving stability control systems (ESP) for governing and limiting undesirable yaw movements about the vertical axis are known in the art. Essential quantities that can be varied deliberately by the driver are measured by means of sensors whereby to calculate a nominal yaw rate. The quantities refer to the steering angle, the accelerator pedal position, the braking pressure, the transverse acceleration, and the rotational behavior of the individual vehicle wheels. In addition, the actual value of the yaw rate developing as a reaction to the driving maneuver is measured using a yaw rate sensor. If the actual value of the yaw movement differs from the calculated nominal value by a predetermined amount jeopardizing driving stability, the yaw movement is limited to allowable values by a specified brake and engine intervention.
This demands a high degree of functional safety from the sensors because their malfunctions may effect, under certain circumstances, braking actions or a neutralization of braking effects at a wrong point of time, thereby potentially triggering dangerous situations. This is especially applicable to a yaw rate sensor in which a moderate exceeding of allowable drift tolerances for accuracy and precision may cause undesirable control actions. Although the effect of the control actions is governed by using other auxiliary variables, causalities, or plausibility criteria, the major endeavor of the automotive industry is to increase the inherent safety of yaw rate sensors so that undesirable control actions, caused by faulty yaw rate sensors, can be prevented reliably even without other auxiliary quantities, causalities, or plausibility criteria. State of the art yaw rate sensors for automotive vehicles provide a high degree of inherent safety and are designed such that a defined total failure becomes apparent in the majority of cases. However, there is still some likelihood that possible, slowly proceeding defects will not be detected. Such defects can be the result of faulty capacitors, open high-ohmic semiconductor inputs, intermittent contacts, etc. The likelihood of a sensor failing can be indicated on the part of the manufacturer for an isolated sensor. However, this so-called inherent safety of the sensor does not meet with the demands of automotive vehicle industry.
A failure limit requirement can be estimated according to the following calculation. The estimation that 10 million vehicles are produced and supplied per year, and with an average service life of 4500 hours per vehicle, leads to a demanded failure probability of the yaw rate sensor or 10−7 approximately.
Presently, conventional yaw rate sensors for automotive vehicles do not satisfy these high demands placed on such a low failure probability. Therefore, there is a need to provide a unit for yaw rate sensor systems with a high degree of inherent safety.